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AJP - Regulatory, Integrative and Comparative Physiology 302 (2012) R929-R940
Hormonal responses to extreme fasting in subantarctic fur seal (Arctocephalus tropicalis) pups.
Delphine Verrier1, 2, Shannon Atkinson3, Christophe Guinet4, Rene Groscolas2, John Py Arnould5

Surviving prolonged fasting implies closely regulated alterations in fuel provisioning to meet metabolic requirements while preserving homeostasis. Little is known, however, of the endocrine regulations governing such metabolic adaptations in naturally fasting free-ranging animals. The hormonal responses to natural prolonged fasting, and how they correlate to the metabolic adaptations observed, were investigated in subantarctic fur seal (Arctocephalus tropicalis) pups, which, due to the intermittent pattern of maternal attendance, repeatedly endure exceptionally long fasting episodes throughout their development (1-3 months). Phase I fasting was characterized by a dramatic decrease in plasma insulin, glucagon, leptin and total T(4) associated with reductions in mass-specific RMR, plasma triglycerides, glycerol and U:C, while NEFA and β-OHB increased. In contrast, the metabolic steady-state of Phase II fasting reached within 6 days was associated with minimal concentrations of insulin, glucagon and leptin, unchanged cortisol and T(3), and moderately increased T(4). The early fall in insulin and leptin may mediate the shift to the strategy of energy conservation, protein sparing and primary reliance on body lipids observed in response to the cessation of feeding. In contrast to the typical mammalian starvation response, non-elevated cortisol and minimal glucagon levels may contribute to body protein preservation and downregulation of catabolic pathways in general. Furthermore, thyroid hormones may be involved in a process of energy conservation independent of pups' nutritional state. These original hormonal settings might reflect an adaptation to the otariid repeated fasting pattern and emphasize the crucial importance of a tight physiological control over metabolism to survive extreme energetic constraints.
1 :  University of Melbourne - Department of Zoology
2 :  DEPE-IPHC - Département Ecologie, Physiologie et Ethologie
3 :  University of Alaska Fairbanks - School of Fisheries and Ocean Sciences
4 :  CEBC - Centre d'études biologiques de Chizé
5 :  School of Life and Environmental Sciences
Sciences de l'environnement
starvation - leptin - cortisol - thyroid hormones - insulin